Deprecate overloaded process method

main-command/src/main/scala/sbt/Command.scala

@@ -185,7 +185,9 @@ object Command {
     )
 
   // overload instead of default parameter to keep binary compatibility
+  @deprecated("Use overload that takes the onParseError callback", since = "1.9.4")
   def process(command: String, state: State): State = process(command, state, _ => ())
+
   def process(command: String, state: State, onParseError: String => Unit): State = {
     (if (command.contains(";")) parse(command, state.combinedParser)
     else parse(command, state.nonMultiParser)) match {